A significant recent advance in the science of dental materials has been the availability of composite-resin plastic materials such as disclosed in U.S. Pat. Nos. 3,629,187, 3,709,866, 3,835,090, and 3,845,009. These materials are useful in restoring the natural shape and function of a tooth which has been damaged by decay or fracture resulting in loss of some of the natural tooth structure.
The damaged tooth is prepared by conventional drilling and grinding techniques to remove carious material and to provide anchorage for the restoration material. The composite resin is then applied in a viscous state to the prepared tooth and allowed to set to a hard condition. These restorative materials are useful on either primary or permanent teeth, and are principally applied to anterior teeth which do not bear the heavy crushing loads to which the occlusal surfaces of molar teeth are subjected during chewing of food.
Crown forms or so-called strip crowns are known, and these forms serve as molds to hold and shape the restoration material during application to and setting or curing on the prepared tooth. Typical commercially available crown forms are a thin shell-like hollow body shaped to correspond to a specific natural tooth and made of cellulose-acetate materials. A generally cylindrical extension is typically formed at the gingival or base end of the body, and this extension and the body are trimmed as necessary to provide a good fit on the prepared tooth.
The crown form is partially filled with the compositeresin restorative material, and is then fitted over the prepared tooth to pack the composite material against the tooth and the interior surface of the form. Any surplus material is vented and removed, and the remaining material is molded by the form into a natural tooth-crown shape and supported in this shape until the material hardens. The wall of the form is then cut, and the form is stripped away from the tooth and restoration material. The restoration is completed by conventional grinding and polishing to insure conformance to a natural tooth shape.
Several problems are encountered in the use of these conventional "strip" crowns. The cellulose-acetate material used in prior-art crowns is prone to slump and deform during storage, requiring special packaging techniques and possible re-shaping prior to use. This material also tends to adhere to the hardened restoration, and is difficult to peel from the restoration in a single operation. These crowns are also awkward and difficult to hold without distortion when being partially filled with the restoration material and during installation on the prepared tooth. Prior-art crowns are further typically unmarked as to the tooth of intended use, leading to a problem of sorting and identifying any units which have been removed from marked storage containers.
The crown form of this invention is an improvement over known strip crowns in both shape and material. The new crown form is made of a co-polyester plastic which has good shape-retaining properties, and is readily stripped as a unit from the cured restoration material. An important feature is the provision of an integrally molded tab at the gingival end of the crown form to serve as both a handle and a flat surface for displaying tooth-identification information. A continuous outwardly extending flange is also formed at the gingival end to strengthen and rigidify the crown form.